The present invention relates to a stacked structure having at least two composite layers and a metal layer, this composite layer having a metal matrix and fibers embedded in the matrix. This composite layer, especially, that in which the fibers are selected to have a thermal expansion coefficient lower than that of the metal matrix, preferably, a thermal expansion coefficient equal to or lower than that of a semiconductor material, is satisfactorily used as an electrode plate of a semiconductor device.
The composite layer having a metal matrix and fibers embedded in the former (which composite layer will be referred to simply as the "matrix-fiber composite" hereinafter throughout the specification) is disclosed in detail, by way of example, in U.S. Pat. No. 3,969,754 issued to Kuniya et al. on July 13, 1976, U.S. Pat. No. 4,083,719 issued to Arakawa et al. on Apr. 11, 1978, and U.S. Pat. No. 4,196,442 issued to Kuniya et al. on Apr. 1, 1980, all of which are assigned to the same assignee to that of the present invention. With reference to those U.S. Patents, the general structures, materials, fabrications, applications, advantages and so on of the matrix-fiber composite will be understood by those skilled in the art.
In the only one layer of matrix-fiber composite member to be sandwiched between two members which have thermal expansion coefficients .alpha. largely different from each other, e.g., two plates which are made of copper (.alpha.: 16.5.times.10.sup.-6 /.degree.C.) and silicon (.alpha.: 3.5.times.10.sup.-6 /.degree.C.), according to the prior art, there has been known a device, in which the distribution of the fibers in the matrix-fibered composite is not homogeneous but the fibers are distributed more in the vicinity of the silicon plate than in the vicinity of the copper plate (See column 3, lines 11 through 17, and column 4, lines 34 to 44 of U.S. Pat. No. 3,969,754). By the aforementioned device, the thermal expansion coefficient .alpha. of the matrix-fiber composite is gradually varied in the thicknesswise direction to reduce the thermal distortion.
As a matter of fact, however, it is difficult to fabricate the matrix-fiber composite such that the distribution of the fibers is gradually varied. Moreover, if that fabrication should be possible, the result is that the thermal expansion coefficient .alpha. is largely different between the portions in the vicinity of the paired major surfaces of the matrix-fiber composite, respectively. We, the inventors, have therefore found that there arises a problem that warping takes place in the matrix-fiber composite itself. This warping is propagated to a semiconductor chip, which is to be connected with and placed on the matrix-fiber composite, thereby to invite a fear that the electrical characteristics of the semiconductor device are deteriorated.